The invention relates to coke ovens and in particular to methods and apparatus for operating coke ovens which improve oven life, reduce emissions and increase coke yield from the ovens.
Coke is a solid carbon fuel and carbon source used to melt and reduce iron ore in the production of steel. During an iron-making process, iron ore, coke, heated air and limestone or other fluxes are fed into a blast furnace. The heated air causes combustion of the coke which provides heat and a source of carbon for reducing iron oxides to iron. Limestone or other fluxes may be added to react with and remove the acidic impurities, called slag, from the molten iron. The limestone-impurities float to the top of the molten iron and are skimmed off.
In one process, known as the xe2x80x9cThompson Coking Process,xe2x80x9d coke used for refining metal ores is produced by batch feeding pulverized coal to an oven which is sealed and heated to very high temperatures for 24 to 48 hours under closely controlled atmospheric conditions. Coke ovens have been used for many years to covert coal into metallurgical coke. During the coking process, finely crushed coal is heated under controlled temperature conditions to devolatilize the coal and form a fused mass having a predetermined porosity and strength. Because the production of coke is a batch process, multiple coke ovens are operated simultaneously, hereinafter referred to as a xe2x80x9ccoke oven batteryxe2x80x9d.
At the end of the coking cycle, the finished coke is removed from the oven and quenched with water. The cooled coke may be screened and loaded onto rail cars or trucks for shipment or later use or moved directly to an iron melting furnace.
The melting and fusion process undergone by the coal particles during the heating process is the most important part of the coking process. The degree of melting and degree of assimilation of the coal particles into the molten mass determine the characteristics of the coke produced. In order to produce the strongest coke from a particular coal or coal blend, there is an optimum ratio of reactive to inert entities in the coal. The porosity and strength of the coke are important for the ore refining process and are determined by the coal source and/or method of coking.
Coal particles or a blend of coal particles are charged into hot ovens on a predetermined schedule, and the coal is heated for a predetermined period of time in the ovens in order to remove volatiles from the resulting coke. The coking process is highly dependent on the oven design, the type of coal and conversion temperature used. Ovens are adjusted during the coking process so that each charge of coal is coked out in approximately the same amount of cycle time. Once the coal is coked out, the coke is removed from the oven and quenched with water to cool it below its ignition temperature. The quenching operation must also be carefully controlled so that the coke does not absorb too much moisture. Once it is quenched, the coke is screened and loaded into rail cars or trucks for shipment.
As the sources of high grade coal for coking operations continue to decrease, less desirable coals are being used to produce coke. Such less desirable coals may have variable moisture and volatile matter content which affect the coking operations. Control of the coking operation is important to provide high quality coke for metallurgical processes. There continues to be a need for improved coking processes and apparatus for providing high quality coke.
With regard to the above and other advantages, the invention provides a coke oven battery including at least a first coke oven and a second coke oven adjacent the first coke oven. Each of the first and second coke ovens contains a coking chamber defined by chamber sidewalls, chamber roof and chamber floor, wherein each coking chamber includes a gas space above a coke bed. The chamber floor of the first coke oven is heated by a first sole flue gas system and the chamber floor of the second coke oven is heated by a second sole flue gas system. At least one of the chamber sidewalls between the first and second coke ovens contains at least one downcomer in flow communication between the gas space of the first coking chamber and the first sole flue gas system for directing flue gases from the gas space of the first coking chamber to the first sole flue gas system. The coke oven battery also contains a connecting gas conduit in gas flow communication between the gas space of the first coking chamber and the gas space of at least the second coking chamber or the sole flue gas system of at least the second coke oven for directing at least a portion of flue gas from the gas space of the first coking chamber to the second coke oven in order to reduce a gas flow rate in the first sole flue gas system.
In another aspect the invention provides a flue gas sharing system for a coke oven battery containing at least a first coke oven and a second coke oven. The first coke oven has a first sole flue gas system, a first coking chamber and a first gas space above a coke bed in the first coking chamber. The second coke oven has a second sole flue gas system, a second coking chamber and a second gas space above a coke bed in the second coking chamber. The flue gas sharing system includes a refractory lined duct in gas flow communication between the first gas space and at least the second gas space or the second sole flue gas system whereby a flue gas flow rate in the first sole flue gas system is reduced compared to a flue gas flow rate in the first sole flue gas system in the absence of the refractory lined duct.
In yet another aspect the invention provides a method for decreasing gas flow rates in a sole flue gas system for a coke oven during at least an initial coking operation after charging a coking oven with coal. The method includes providing a duct system between a first coke oven having a first coking chamber, a first gas space above a first coke bed and a first sole flue gas system and a second coke oven having a second coking chamber, a second gas space above a second coke bed and a second sole flue gas system to direct at least a portion of gas in the first gas space to at least the second gas space or the second sole flue gas system for the second coke oven thereby reducing a gas flow rate in the first sole flue gas system.
The invention provides a unique system for reducing peak oven temperatures and gas flow rates in coking chambers in order to prolong the life of the refractory lined ovens and to further reduce undesirable emissions from the coking operation. The system is adaptable to use with at least two coke ovens and may be used with three or more the coke ovens in a coke oven battery. Furthermore, the system is readily adaptable to existing coke ovens without major modifications of the ovens and without substantial changes in coke oven operations.
As will be described in more detail below, coke oven temperatures are dependent on the quality of coal, the amount of coal charged to the oven and the amount of combustion air provided to the oven. From a practical point of view, prior to the invention, the only way to control peak oven temperature was to reduce the charge of coal to the oven for a given coal source. A coal high in volatiles results in the need for additional combustion air being provided to an oven to assure complete combustion of the volatiles. However, the amount of combustion air provided to an oven is limited by the natural or induced draft system for the coke battery. Additional combustion air reduces the natural or induced draft in a coke oven battery and may result in increased emissions from the ovens during charging and coking operations. The invention provides a unique means for operating a coke oven battery so that increased coke production may be achieved.